Thesis supervisor: János Józsa
Location of studies (in Hungarian): BME Vízépítési és Vízgazdálkodási Tanszék Abbreviation of location of studies: BMEVV
Description of the research topic:
The flow features, physical characteristics and quantity of sediment transport, the composition and dynamic nature of the bed material all play an important role in the quality of riverine habitats and its suitability for different fish species. There can be several recent studies found dealing with the linking of abiotic, so called hydro-morphological parameters to the biotic indicators, e.g. the abundance of fish and benthic fauna. The so called eco-hydraulic assessment of rivers addresses this topic, i.e. the interconnected analysis of abiotic and biotic indicators. The hydro-morphological characterization of Hungarian rivers is only in the preliminary stage. One of the reasons of this is that abundance assessment of fishes and other benthic species is far not straightforward, moreover, the detailed investigation of nearbed flow features can hardly be performed, especially in large rivers. One of the goals of the proposed PhD research is to gain new insights into the hydro-morphological processes at the benthic zone, which enables a more accurate micro-scale characterization of the habitats. Based on the improved understanding of the nearbed flow features, an upscaling of the local scale information can lead to the spatial extension of the characterization towards a meso-scale description. The meso-scale habitat assessment of rivers can provide practical, tangible results of the research.
In detail:
Hydro-morphological indicators play an important role in the behavior of fish, selection of spawning places, hiding, habitat selection of invertebrates as well as in their longitudinal and transversal distribution in rivers. One of the most decisive, but at the same time hardly measurable, physical parameters is the turbulent boundary layer at the river bed and the bed shear stress. The nearbed turbulence is governed by the composition, the stability, stratification as well as other physical parameters of the river bed and its interaction with the flow field. The quantitative assessment of this parameter, especially in large rivers, is challenging and therefore, rather indirect estimation methods are used, based on e.g. the measured distribution of the flow velocities along a vertical of the river, or using computational simulation tools. However, the application of existing acoustic velocimeters with suitable measurement infrastructure might be capable for direct measurement of nearbed turbulence, e.g. the turbulent kinetic energy or Reynolds-stresses, even in large rivers.
One of the tasks of the candidate is test such a measurement approach in the field. It is expected that more accurate, novel insight can be gained about the local turbulence features and about its spatial and flow-dependent variation. The measurement campaigns shall be carried out in a suitable, sand-gravel bed section of the Danube River, at one of the study sites of the host department. Within the frame of the scientific cooperation between the host department and the Centre for Ecological Research, Hungarian Academy of Sciences (MTA-ÖK) the candidate has the opportunity to join a Danube-wide field campaign which aims at the habitat assessment of the Hungarian section of the river, which at the same time will provide new knowledge about the suitability of the habitats. Exploiting the results from the field campaign, with complementary hydro-morphological measurements, the improvement of existing reach scale mesohabitat evaluation models can be proposed.
Proposed subtasks:
• Overview of recently published micro- and mesoscale habitat evaluation models
• Overview of the relevant hydro-morphological parameters in the models, and the analysis of measurability and simulatability of the parameters
• Overview of the measurement methodologies of nearbed turbulence and establishment of a method to be applied in the study site in the Danube River
• Implementation of field measurement campaigns, for which the complementary bathymetry, sediment and bed material samplings will be performed by the host department
• Quantitative assessment of nearbed turbulence for different flow conditions and comparative analysis with other indirect methods
• Participation in field habitat evaluation campaigns at the Danube River in cooperation with MTA-ÖK
• Based on the field habitat assessment and the novel findings in nearbed turbulence, recommendations shall be made for the improvement of meso-scale habitat evaluation models
Number of students who can be accepted: 1
Deadline for application: 2018-12-20
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
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